This invention relates to an analytical method for particulate substances and relevant analytical equipment, as well as to its application system, and especially relates to the analytical method and the relevant analytical equipment as well as to its application system which is advantageous for exclusively analyzing particulate substances contained in liquid or gas (for instance, determining the particle-count of particulate substances contained in the liquid, while not erroneously counting air bubbles.)
An existing analytical method is described in the laid-open patent application: SHO 62-38345 relating to an analytical method for particulate substances in liquids using photoacoustic spectroscopy. This conventional photoacoustic spectroscopy works in such a way that the particulate substances contained in a fluid sample are irradiated with light to generate heat energy with provisions arranged to prevent the generation of acoustic waves, and the heat energy generated converts into acoustic waves which are continuously detected to represent the particle-count in a fluid sample. It has been revealed by the work of the inventors, though the cited literature did not state such clearly, that the acoustic waves generated at a high irradiation intensity were those caused by optical breakdown.
This invention relates to a method of detecting particulate substances on the basis of the optical breakdown of particles, and according to the inventors' work, it is a new finding whereby the threshold value for the optical breakdown of the particles is smaller than the threshold value for the optical breakdown of liquid or air, details of which are given herein.
However, this fact was not perceived in the conventional analytical method, and the irradiating light intensity or the power density was not set at a high enough value above the threshold value of the breakdown in comparison with the particles or low enough below the threshold value of the breakdown in comparison with the media or air bubbles. That is to say, in the conventional analytical method, the power density of irradiating light was sometimes one that generates no acoustic waves breakdown the particles, or sometimes one which induces breakdown not only of particle but also of media or air bubbles. Therefore, the aforementioned conventional technology cannot induce the selective breakdown of particles. Accordingly, the reliability of the measured results was low because miscounts for air bubbles or the like were included.
Furthermore, there is a description in the laid-open patent application: SHO 62-38345, that the method offers the possibility of analyzing the components of the particle on the basis of the dependency of the signal magnitude upon wave length, using a variable wave length-type high-power laser unit. However, the component analysis of the particle described was impossible because of the difficulty of obtaining particular signals representing the proper characters of the components consisting of individual particles, for the reason that the conventional technology was a component analysis based on the absorption spectrum of the whole sample existing in the irradiated area.